Electric motor control



Nov. 17, 1936. R. G. LOCKETT 2,060,997

ELECTRIC MOTOR CONTROL Filed Oct. 12, 1935 Patented Nov. 17, 1936 PATENT- OFFICE 2,060,997 amcrmc MOTOR comor.

Ralph Lockett, Cutler-Hammer, poration of Delaware Wauwam, Wis aaaignor to Inc., Milwaukee, Wis., a cor- Application October 12, 1935, Serial No. 44,643

10 Claims. (01. 112-240) This invention relates to improvements in elec-- tric motor control. The invention relates more particularly to a control system for a reversible electric motor driving a rotatable load of such character as to be self-reversing after coasting thereof to zero speed as an incident to interruption of the motor circuit connections. An object of the invention is to provide novel means for timing completion of reverse circuit connections for a motor driving a load of the character aforementioned. whereby excessive speed of the motor at of the reverse circuit connections is avoided.

Another object is to provide means of the aforementioned character which is simple, efficient and inexpensive.

- A more particular object is .to provide novel means for controlling reversing of a motor driving a load comprising a substantially cylindrical container rotatable upon a horizontal axis, and which container is partially fllled with loose or amorphous material.

Another object is to provide a control system of the aforementioned character having the desired features of manual and automatic control. other objects and advantages of the invention will hereinafter appear.

The accompanying drawing illustrates schematically and diagrammatically an embodiment of the invention which will now be described,--it being understood that the embodiment illustrated is susceptible of modification as to certain details thereof without departing from the scope of the appended claims.

I have illustrated my invention as applied to the control of a reversible motor driving a cylinder or container which is rotatable upon a horizontal axis,-such as is used in the melting industry to dry or otherwise treat large quantities of loose or amorphous material such as cereal or grain. As will be apparent to those skilled in the art, however, the invention is likewise applicable to the control of reversible motors driving loads of other material of a loose ,or amorphous character,as for instance the cylindrical containers used by the laundry industry for clothes washing and/or drying machines.

In a device of this character it is desired to rotate the cylinder a predetermined number of times in one direction,-any suitable or desired timing means, such as a limitswitch of the double throw type, being employed to effect interruption ofthe energizing circuit of the active reversing switch. Heretofore it has been customary to al-= low the cylinder to coast for a short period of the moment of completion time as preselected by adjustment of a timing relay,-the timing relay when, operated being adapted to bring in the other reversing switch to effect reversal of the motor and the cylinder driven thereby. However, it has been found in practice that the machine comes to zero speed quite rapidly due to the weight of the cereal or similar loose or amorphous material which builds up inside of the drum or cylinder. In many instances it was found that theequipment actually reversed before the reversing contactor was closed by the timing relay,--w,ith the result that very often the motor was driven over-speed by the cylinder. In such cases when the motor is energized and thereafter brought 'down to normal speed there is quite a shock upon the machinery,-and it is even likely that the motor may be driven temporarily at such an excessive speed as to injure or wreck the same mechanically. I

From the foregoing it will be apparent that it is very important that the reversing contactor be brought in at a point close to zero speed of the cylinder; or, in other words, immediately after zero speed has been attained by the cylinder, and before any substantial degree of reverse rotation thereof by its self-reversing action aforementioned. A fixed timing for the coasting period obviously is not suitablebecause the load varies considerably from time to time, and the length of the coasting period desired varies correspondingly. The aforementioned defects and disadvantages of prior devices are overcome or avoided by my invention.

Referring to the drawing, the numeral 5 designates a cylinder or drum which is rotatable upon a horizontal axis as by means of a reversible electric motor 6. Motor 8 is preferably of standard squirrel cage type, and suitable speed-reducing gearing l is preferably interposed between the armature shaft 8 thereof and the shaft 9 of cylinder 5. Cylinder 5 is provided with an opening, the door or closure for which is shown diagrammatically at it, to provide for partially filling the cylinder with cereal or similar loose or amorphous material; as, for instance, to the level indicated by the dotted line l l. Motor 8 is adapted to be supplied with current source of supply, represented by lines L L and L through the medium of a pair of electromagnetically operable reversing switches I2 and It. The operating windings l2 and I3 of switches l2 and it are respectively subjected to control by the limit switches it and l5,-the latter being from a suitable mechanically connected, as by means of the pivoted link It, to insure Joint operation thereof.

The shaft 9 of cylinder 5 is provided with a threaded extension 9 which is adapted to cooperatively engage a pair of traveling nuts I! and |8,a guide rod or plate |9 being adapted to restrain said nuts against rotation. The arrangement is such that upon a predetermined number of revolutions of cylinder 5 in one direction the nut It will engage switch It to effect opening thereof, while the link I3 acts to simultaneously eilect closure of switch |4,an over-center spring 20 being provided to insure snap movements of switches l4 and I5 between opposite extreme positions thereof. Upon reversal of the direction of rotation 01' cylinder 5 nuts i1 and I3 will travel toward the left, until nut i1 engages switch H to eil'ect opening thereoi.',link l6 acting in the manner aforedescribed to simultaneously eiiect closure of switch it.

One or the other of the limit switches l4 and I9 is initially rendered eflective for completing an energizing circuit for the winding i2 or 3 respectively associated therewith by closure sia pair of normally open electromagnetically operable relays 2| and '22; 2 operating winding 2| and sets of contacts 'fl 2|, and relay 22 having an op crating winding 22 and sets 01' contacts 22'', 22. Energization and closure 01' relays 2| and 22 is effected by momentary closure of a normally open Push button switch 23.

Thus with the several parts in the positions thereoi' illustrated, the equipment may be started in operation by momentarily depressing the push button 23'.

traced from line L through contacts 23, 23 and 23 of switch 23, by conductor 29'thmugh the winding 2|. oi! relay 2|, and by conductors 21 and 29 to line I). The normally open contacts 2|, 2| oi relay 2| are thus closed.. At the same time an energizing circuit is completed tor the winding of relay 22, which circuit may be traced from line I.- by conductors switch 23, by conductors 29 and 39 through the contacts oi a normally closed push button switch 3|, by conductor 32 through the winding 22 01' relay 22, and by conductors 33 and 28 to line I The normally open contacts 22" and 22 of relay 22 are thus closed.

an energizing circuit for .the operating winding oi reversing switch 3 is thus completed, which circuit may be traced from line L by conductors 24 and. 34 through contacts 22 of relay 22, by conductor 39 through contacts 2| of relay 2|, conductor 39 through limit switch II, conductor 31 through said winding -l3, and by conductors 39 and 23 to line L, whereupon the contacts l3, |3, I3 of switch |3 are closed to provide for operation of motor 6 and container 9 in a direction such as to cause movement of nut it toward the right.

In accordance with my invention there is provided a switch 39 comprising an oscillatable contactor 39 and a pair 01' contacts 39'. 39 to be selectively engaged thereby,depending upon the direction of operation of motor 9 and container I driven thereby. For this purpose the armature motor 9 is shown as provided with an extension 8 to which a pulley or wheel 39 is keyed or otherwise rigidly secured. Exten around and i'rictionally engaged with wheel 39 is a belt or strap 39, the opposite ends. of which being noted that the energizing circuit for are rigidly attached to contactor 39 on opposite sides of the point of pivotal support of the latter. Suitable means (not shown) are provided for insuring the desired degree 01' tension of belt 39 against wheel 39. A switch of the general character illustrated at 39 is shown and described in detail in Patent No. 1,964,199, granted June 26, 1934, to C. T. Evans.

It is to be understood that with motor 9 and container 9 operating in a direction to eiiect movement of nut I8 toward the right (as indicated by the arrows on shafts 3 and 9) the contactor 39 of switch 39 will beengaged with contact 39 ,-thus providing for the winding l3 of reversing switch l3 a maintainingcircuit which shunts the contacts 2| of relay 2|. It is therefore obvious that after push button 23 the same may be released to permit de-energization and opening of relay 2|,it relay 22 when completed is self-maintained by a circuit which may be traced from line L by conductors 24 and 34 through contacts 22, 22" 01' relay 22, by conductors 49 and 39 through switch 3|, conductor 32 through the winding 22, and by conductors 33 and 23 to line L.

The ai'oredescribed maintaining circuit for the winding i3 oi! switch |3 may be traced from line L by conductors 24 and 34, through contacts 22 oi relay 22, conductor 33 through contactor 33 and contact 39 of switch 39, conductors 4| "and 36 through limit switch ll, conductor 31 through said winding l3, and conductors 33 and 23 to line L I In view 0! the tact that contactor 39 is normally in one or the other of its extreme positions, it is obvious that if desired the relay 2| might be entirely omitted. Relay 2| has been shown herein as providing means for positively insuring ability to start the system in operation at will,

even though the contactor 33 oi switch 39 should accidentally remain in an intermediate position 3| momentarily, thus interrupting the maintaining circuit for the winding 22 of relay 22.

Pending depression of push button switch 3| engagement of contactor 39 of switch 39 with the stationary contact 39. Contactor 39 will, however, remain in engagement with contact 39' such manner that ment with contact 39.

An energizing circuit for the winding l2 of reversing switch I2 is thus completed, said circuit extending Irom line L by conductors 24 and through contacts 22 of relay- 22, conductor 35 through contactor 39" and contact 39 of switch 39, conductors 42 and 43 through limit switch H, conductor 44 through said winding I2 of reversing switch l2, and by conductors 45, 38 and 28 to line L Contacts l2", l2, l2 of switch l2 are thus closed to effect reverse operation of motor 6 and cylinder 5 with the load contained in the latter. The reverse circuit connections for motor 6 are thus completed almost immediately after the self-reversing movement of container 5 which is incidental to the aforedescribed character of the material contained within the latter, whereby excessive initial speed of the motor armature is avoided.

The aforedescribed cycle of operations is repeated automatically until it is desired to shut down the entire system. Such a shut down may be effected at will by momentarily depressing the push button switch 3| which effects de-energization of the operating winding 22 of relay 22 and opening of the contacts 22", 22 of the latter,- thus likewise insuring de-energization of one or the other of the windings ll or i3 of reversing switches l2 and I3 (whichever one was active), and insuring against re-energization thereof pending momentary reclosure of push button switch 23 as aforedescribed.

In the melting industry, the grain is delivered to and taken from the rotating drum while the drum is in motion through suitable chutes at the ends. Thus it is possible for the operator in normal operation to insure that the load is reduced suitably before depressing the stop button, to avoid excessive speed on the motor when driven by the load.

When desired an electromagneticallyreleasable brake may be employed-the releasing winding thereof being adapted to be de-energized and the shoe thereof applied by spring or weight upon depression of the 'stop button 3l,--thereby insuring against excessive overhauling action of the motor by the load.

What I claim as new and desire to secure by Letters Patent is:

1. In a control system of the character described, in combination, a substantially cylindrical container rotatable upon a horizontal axis, said container having therein an amount of amorphous material less than that required to completely fill the same, a reversible electric motor having a driving connection with said container, means for completing an energizing circuit for said motor whereby said container is rotated in one direction, means including a limit switch operable automatically to effect interruption of said motor circuit, said container being thereupon adapted to coast pending attainment of zero speed of rotation thereof in the direction aforementioned, whereupon the position of the material within said container serves to automatically initiate rotation of the latter in the reverse direction, a switch comprising a stationary contact and an oscillatable contactor, and means including a frictional driving connection between said container and said contactor whereby the latter is engaged with said contact immediately upon reversal of the former in the manner aforementioned, said contactor when engaged with said contact being adapted to effect completion of an alternative energizing circuit for said motor whereby the latter is adapted to drive said container in the reverse direction thereof so initiated.

2. In a control system of the character described, in combination, a substantially cylindrical container rotatable upon a horizontal axis, said container having therein an amount of amorphous material less than that required to completely fill the same, a reversible electric motor having a. driving connection with said container, means for completing an energizing circuit for said motor whereby said container is rotated in one direction, means including a limit switch operable automatically to effect interruption of said motor circuit, said container being thereupon adapted to coast pending attainment of zero speed of rotation thereof in the direction aforementioned, whereupon the position of the material within said container serves to automatically initiate rotation of the latter in the reverse direction, a switch comprising a stationary contact and an oscillatable contactor, means including a frictional driving connection between said container and said contactor whereby the latter is engaged with said contact immediately upon reversal of the former in the manner aforementioned, said contactor when engaged with said contact being adapted to efiect completion of an alternative energizing circuit for said motor whereby the latter is adapted to drive said container in the reverse direction thereof so initiated, and means including a second limit switch operable automatically to effect interruption of said alternative energizing circuit for the motor upon a predetermined number of rotations of said container in the direction thereof last mentioned.

3. In a control system of the character described, in combination, a substantially cylindrical container rotatable upon a horizontal axis, said container having therein an amount of amorphous material less than that required to completely fill the same, a reversible electric motor having a driving'connection with said container, means for completing an energizing circuit for said motor whereby said container is rotated in one direction, means including a limit switch operable automatically to effect interruption of said motor circuit, said container being thereupon adapted to coast pending attainment of zero speed of rotation thereof in the direction aforementioned, whereupon the position of the material within said container serves to automatically initiate rotation of the latter in the reverse direction, a switch comprising a stationary contact and an oscillatable contactor, means including a frictional driving connection between said container and said contactor whereby the latter is engaged with said contact immediately upon reversal of the former in the manner aforementioned, said contactor when engaged with said contact being adapted to effect completion of an alternative energizing circuit for said motor whereby the latter is adapted to drive said container in the reverse direction thereof so initiated, means including a second limit switch operable automatically to effect interruption of said alternative energizing circuit for the motor upon a predetermined number of rotations of said container in the direction thereof last mentioned, and means for positively interlocking said limit. switches to insure closure of each upon opening of the other of same.

4. In a control system of the character described, in combination, a substantially cylindrical container rotatable upon a horizontal axis, said container having therein an amount of amorphous material less than that required to completely fill the same, a reversible electric motor having a driving connection with said container, means for completing an energizing circuit for said motor whereby said container is rotated in one direction, means including a limit switch operable automatically to elect interruption of said motor circuit, said container being thereupon adapted to coast pending attainment of zero speed of rotation thereof in the direction aforementioned, whereupon the position of the material within said container serves to automatically initiate rotation of the latter in the reverse direction, a switch comprising astationary contact and an oscillatable contactor, means including a frictional driving connection between said container and said contactor whereby the latter is engaged with said contact immediately upon reversal of the former in the manner aforementioned, said contactor when engaged with said contact being adapted to efl'ect completion of an alternative energizing circuit for said motor whereby the latter is adapted to drive said container in the reverse direction thereof so inltiated, means including a second limit switch operable automatically to effect interruption of said alternative energizing circuit for the motor upon a predetermined number of rotations of said container in the direction thereof last mentioned, means for positively interlocking said limit switches to insure closure and opening of each upon opening and closure, respectively, of the other of same, and spring means associated with said limit switches to effect movements thereof with a snap action.

5. In a control system of the character described, in combination, a reversible electric motor, a load to be driven thereby in each direction, said load being of such character that it is selfreversing after coasting thereof in either direction as an incident to interruption of the motor circuit connections, a pair of normally open electromagnetically operable switches, one of said switches being adapted upon energization and closure thereof to effect completion of a circuit for operation of said motor in one direction, a limit switch operable upon a given number of 1 rotations of said load to effect de-energization and opening of said last mentioned electromagnetically operable switch whereby said motor circuit is interrupted, said limit switch being simultaneously operable to preset an energizing circuit for theother of said electromagnetically operable switches for completion thereof upon selfreversal of the direction of rotation of said load after coasting of the latter, the means for effecting completion of said last mentioned circuit including a switch having a pair of stationary contacts and a pivoted contactor movable into engagement with one or the other of said contacts, depending upon the direction of rotation of said load, and said means including a frictional driving connection between said motor and said contactor.

6. In a control system of the character described, in combination, a substantially cylindrical container rotatable upon a horizontal axis, said container being adapted to receive an amount of loose material less than that required to completely fill the same, an electric motor having a positive driving connection with said container, a pair of normally open electromagnetically operable switches respectively adapted when closed to provide circuit connections for forward and reverse operation of said motor, means for insuring closure and opening of the respective switches in sequence to effect periodic reversal of the direction of operation of said motor, said means comprising a pair of limit switches each having a pivoted contactor and an associated stationary contact, said contactors being mechanically interlocked to insure against simultaneous engagement thereof with said contacts, a pair of traveling nuts associated with said container and operable to sequentially eii'ect opening of each of said limit switches while simultaneously eii'ecting closure oi the other of same upon like periods of rotation of said container in opposite directions respectively, each of said limit switches when closed being ineffective for completing an energizing circuit for its associated electro-magnetically operable switch pending operation of a direction-responsive switch common to said limit switches, said direction-responsive switch comprising a pair of spaced stationary contacts and an oscillatable contactor associated therewith, a frictional driving connection interposed between said container and saidcontactor whereby the latter is engageable with said stationary contacts alternately as an incident to reversal of the direction of rotation of said container, the arrangement being such that upon a given degree of coasting of said container in a given direction after interruption of the motor circuit connections the material within the container will be so positioned as to effect initiation of operation of said container in the reverse direction, such reverse operation of the container being adapted to effect engagement of the direction-switch contactor with one of its associated contacts whereby the limit switch then in closed position is rendered effective for completing an energizing circuit for its associated electromagnetically operable switch, whereby an alternative motor circuit is completed to effect positive driving of said container in the direction thereof last mentioned.

7. In a device of the character described, in combination, a reversible driving motor, a load to be rotatably driven thereby in each direction, said load being of such character that it is self-reversing after coasting thereof as an incident to interruption of the motor circuit connections, a pair of electromagnetically operable reversing switches for controlling the direction of operation of said motor, means for selectively effecting energization of said switches after each coasting period of said load to provide for substantially immediate positive driving of said load in the self-reversed direction of rotation thereof, said means comprising an oscillatable contactor, a pair of contacts to be selectively engaged thereby, and means providing a friction driving connection between said load and said contactor, whereby the latter is moved alternately from each extreme position thereof to the other only upon the respective self-reversing operations of said load.

8. In a protective device for a reversible electric motor driving a rotatable load which is self-reversing upon attainment of zero speed after rotation thereof in a given direction, in combination, a reversible electric driving motor, a pair of electromagnetically operable reversing switches adapted when energized selectively to alternately provide reverse circuit connections for said motor, a load to be driven by said motor, said load comprising a cylindrical container mounted upon a horizontal axis, said container having therein a quantity of amorphous material less than that required to entirely fill the same, means including manually operable means for initially effecting energization and closure of one or the other of said reversing switches to provide for rotation of said load in one direction by said motor, means comprising a limit switch operable upon a predetermined number of rotations of said load to eifeet deenergization of said reversing switch with consequent interruption of the motor circuit connections, whereupon said motor and said load are adapted to coast to zero speed thereof in the direction aforementioned, switching means comprising a contact element movable in opposite directions between given circuit controlling positions, means comprising a frictional driving connection between said rotatable load and said con tact element, whereby said contact element is moved from one circuit controlling position thereof to the other as an incident to the self-reversing operation of said load, and means adapted upon such movement of said contact element to automatically effect energization and closure of the other of said reversing switches, whereby immediate reverse operation of said driving motor is effected, to thereby insure completion or" the rea verse circuit connections for said motor at substantially zero speed of said load in said reverse direction.

9. In a protective device for a reversible electric motor driving a rotatable load which is selfreversing upon attainment of zero speed after rotation thereof in a given direction, in combination, a reversible electric driving motor, a pair of electromagnetically operable reversing switches adapted when energized selectively to alternately provide reverse circuit connections for said motor, a load to be driven by said motor, said load comprising a cylindrical container mounted upon a horizontal axis, said container having therein a quantity of loose material less than that required to entirely fill the same, means including manually operable means for initially effecting energizetion and closure of one or the other of said re= versing switches to provide for rotation of said load in one direction by said motor, means comprising a limit switch operable upon a predetermined number of rotations of said load to eflect deenergization of said reversing switch with consequent interruption of the motor circuit connections, whereupon said motor and said load are adapted to coast to zero speed-thereof in the direction aforementioned, switching means comprising a contact element movable in opposite directions between given circuit controlling positions, means comprising a frictional driving connection between said rotatable load and said contact element, whereby said contact element is moved from one circuit controlling position thereof to the other as an incident to the self-reversing operation of said load, means adapted upon such movement of said contact element to automatically efiect energization and closure of the other of said reversing switches, whereby immediate reverse operation of said driving motor is eflected,

to thereby insure completion or the reverse circuit connections for said motor at substantially zero speed of said load in said reverse direction, said limit switch also acting upon a given number tioned reversing switch, whereby the operating cycle aforedescribed is repeated.

10. In a protective device for a reversible electric motor driving a rotatable load which is selfreversing upon attainment of zero speed after rotation thereof in a given direction, in combination, a reversible electric driving motor, a pair of electromagnetically operable reversing switches adapted when energized selectively to alternately provide reverse circuit connections for said motor, a load to be driven by said motor, said load comprising a cylindrical container mounted upon a horizontal axis, said container having therein a quantity of loose material less than that required to entirely fill the same, means including manual- 1y operable means for initially efiecting energizetion and closure of one or the other of said reversing switches to provide for rotation of said load in one direction by said motor, means comprising a limit switch operable upon a predetermined number of rotations of said load to effect deenergization of said reversing switch with consequent interruption of the motor circuit connections, whereupon said motor and said load are adapted to coast to zero speed thereof in the direction aforementioned, switching means comprising a contact element movable in opposite directions between given circuit controlling positions, means comprising a frictional driving connection between said rotatable load and said contact element, whereby said contact element is moved from one circuit controlling position thereof to the other as an incident to the self -reversing operation of said load, means adapted upon such movement of said contact element to automatically effect energization and closure of the other of said reversing switches, whereby immediate reverse operation of said driving motor is efiected,

to thereby insure completion of the reverse circuit connections for said motor at substantially zero speed of said load in said reverse direction,

said limit switch also acting upon a given number of rotations of said load in said reverse direction to effect de-energization of the second mentioned reversing switch with consequent interruption of the motor circuit connections to provide for coasting of said motor and said load, said contact element being operable upon self-reversing of said load to eflect re-energization of said first men- A switch adapted upon opening thereof to effect at will a full stop of said motor and the load driven thereby.

RALPH G. LOCKEI'I. 

